1. Field of the Invention
The present invention relates to a solid-state imaging device, a driving method thereof, and an imaging apparatus, and more particularly, to a solid-state imaging device, a driving method thereof, and an imaging apparatus capable of suppressing generation of a false color or an afterimage at a time when a dynamic range is extended by using image signals of a plurality of exposure periods.
2. Description of the Related Art
Generally, for imaging apparatuses used for monitoring and the like, the characteristic of a wide dynamic range capable of displaying an image from a dark portion to a bright portion without any collapse in imaging a backlight scene, simultaneous indoor and outdoor imaging, or the like is demanded. In order to achieve the characteristic of the wide dynamic range, within a predetermined frame period divided into groups for long time exposure and for short time exposure, read-out of electric charges accumulated during different exposure periods is performed.
FIGS. 26A to 26D represent an operation of related art. In the operation of related art, a long time exposure period and a short time exposure period are arranged for a solid-state imaging device such as a CMOS image sensor, and after image read-out during one exposure period is completed, image read-out during the other exposure period is performed.
FIG. 26A shows a temporal change in signal electric charges accumulated in a photo diode of a pixel of line (n). In addition, FIG. 26B shows the operation of the pixel of the line (n). FIG. 26C shows the operation of a pixel of line (n+1), and FIG. 26D shows an image signal DS. According to a two-time exposure method in which long time exposure and short time exposure are performed, the pixels are swept twice in one video frame period Tf, and thereby two image signals including a signal generated by the long time exposure and a signal generated by the short time exposure are read out. For example, when a long time exposure period Tl is set to a half of the one video frame period Tf, signal electric charges accumulated from time point t90 are read out at time point t91. In addition, at time point when a period acquired by subtracting the long time exposure period Tl and a short time exposure period Ts from the one video frame period Tf elapses, a so-called shutter operation is performed.
In other words, at time point t92 when a period Tn (Tn=Tf−Tl−Ts) elapses from the time point t91, the shutter operation is performed for the accumulated signal electric charges through a reset operation. Thereafter, at time point t93 when the short time exposure period Ts elapses from the time point t92, the accumulated signal electric charges are read out. Such a line read-out operation is sequentially performed from the pixel of the first line. Accordingly, as shown in FIGS. 26B and 26C, a signal of line (n+1) is read out after the read-out of the signal of the line (n). Therefore, as the output of the solid-state imaging device, as shown in FIG. 26D, data of the long time exposure corresponding to one screen and data of the short time exposure corresponding to one screen are alternately output during a period that is a half of the one video frame period Tf.
FIGS. 27A and 27B shows a line from which signal electric charges are read out in the operation of related art. When the read out of the signal electric charges is sequentially performed from the pixel of the first line, at the time point t91, as shown in FIG. 27A, the signal electric charges accumulated by the long time exposure are read out from the pixel of the line (n). In addition, at the time point t93, as shown in FIG. 27B, the signal electric charges accumulated by the short time exposure are read out from the pixel of the line (n). In addition, when the shutter operation is performed in the pixel of line (s), as shown in FIG. 27B, the line (s) is in a position in which the sweeping time is earlier than that of the line (n) by the short time exposure period Ts. In other words, the pixel of the line (s) that performs the shutter operation is set so as to satisfy the condition of “Ts=(s−n)×Th”. Here, “Th” is one horizontal period.
In addition, according to the technology disclosed in JP-2008-99158, in a case where the long time exposure and the short time exposure are performed within a frame period, in resetting the signal electric charges for accumulation of signal electric charges according to the short time exposure, an intermediate voltage is set so as to perform ejection of a part of the signal electric charges. As described above, a part of the signal electric charges is ejected by setting the intermediate voltage. Accordingly, even when the signal electric charges are reset for the short time exposure for a portion of a subject having low luminance, an image signal having a long exposure period is generated without ejecting the accumulated electric charges.